1. Field of the Invention
The present invention relates to a cooling device used for cooling, for example, in a process for manufacturing an electronic or electric apparatus such as an image display panel or a semiconductor device, the cooling device being used after heating a substrate used in the electronic or electric apparatus, as well as an apparatus manufacturing an image display panel using this cooling device and a method for manufacturing a display image panel using the cooling device. More specifically, the present invention relates to a cooling device with which a cooling plate is placed opposite a heated substrate for the electronic or electric apparatus to absorb radiation heat to cool the substrate, as well as an apparatus manufacturing an image display panel using this cooling device and a method for manufacturing a display image panel using the cooling device.
2. Related Background Art
In a conventional process for manufacturing an image display panel or a semiconductor, a substrate is cooled by thermally treating it in a vacuum. The cooling of the heated substrate in the vacuum atmosphere is carried out by absorbing radiation heat (radiant heat) from the substrate. For example, Japanese Patent Application Laid-Open No. H7-216550 discloses a technique in which to cool a substrate in manufacturing a semiconductor, a metal plate is provided parallel with the substrate, while a radiation absorbing layer is formed on a surface opposite to the substrate of the metal plate. The radiation absorbing layer can absorb radiant heat generated by the substrate. Then, the absorbed heat can be transmitted to the metal heat. Moreover, the heat can be discharged via the metal plate.
However, this conventional cooling has problems described below.
First, the temperature of the substrate to be cooled starts to decrease at its peripheral edges, notably in its corner portions, where heat is radiated from its front and back surfaces and side end surfaces. However, an increase in the size of the substrate increases the distance between a central portion and edges of the substrate, thus hindering fast heat transfer. Consequently, there is a large difference in temperature between the peripheral edge, where cooling progresses fast, and the central portion, where cooling is difficult. This temperature distribution associated with the cooling may cause the substrate to be distorted or damaged.
Second, many substrates that require cooling after heating have a member (for example, wiring or phosphor, or the like) provided on a part of a surface of the substrate and which has an emissivity different from that of the substrate itself, for example, as in the case of a substrate (electron source substrate or phosphor substrate) for an image display panel in which an electron source substrate and a phosphor substrate are located opposite each other. A further description will be given taking the case of a substrate for an image display panel. Normally, the substrate is glass, having a relatively high emissivity, and wiring is metal, having a relatively low emissivity. Accordingly, cooling by a cooling plate starts in the vicinities of corner portions of the substrate which are away from an area in which wiring is formed. Thus, disadvantageously, a temperature distribution is created which may cause the substrate to be distorted or damaged. In particular, when the wiring concentrates at a position close to the center of the substrate, the temperature distribution created for the above first reason is further enhanced to crack the substrate.